The Selfridge Collection of Medici manuscripts at Harvard Business School's Baker Library is the largest collection of Renaissance Florentine account books outside Italy. This collection documents both the business and personal economic activities of one branch of the Medici family through six generations, extending from the early fifteenth century through the end of the sixteenth century. It would be difficult to find, even in Florence, another family whose economic activities are so well documented over such a long span of time, a period we know as the Renaissance. This patrimony of family documents was sold by the Medici heirs through an auction at Christie's of London in 1918; and in 1927 the buyer, H. Gordon Selfridge, deposited the ledgers at the Harvard School of Business Administration. Around one hundred ledgers arrived at Harvard at that time, but one item in the Christie's inventory was missing. In 2007, I found this missing item in the catalogue of a Munich antiquarian book dealer, but it had already been sold to a private collector in Germany. When informed of its importance for the Harvard collection, the new owner of the ledger kindly permitted Laura Linard, director of Historical Collections at Baker Library, to have it microfilmed; and so finally, after eighty years, the missing item has returned, at least in a photographic version, to its original home, thereby completing the Selfridge Collection. This event could be the occasion for a reevaluation of a major collection of business documents too long ignored by historians.